i still thnk u should keep the 1k the idea of 1k is a current limiting
resistor and it is a safe way to protect both ur o/p drive to the LED and
the LED itself..
alok


-----Original Message-----
From: David Covick [mailto:dac@WEST.NET]
Sent: Sunday, May 21, 2000 4:08 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: PIC driving LED -- need series R?


Mel,

That depends on the max current of the LED (20 mA).

It just so happens that I am doing the same thing with the 12C671 @ 3V and
sequencing 20 LED's on/off with no R's for the 5 I/O's.

I also do some PWM, which works very nicely from 0 to full brightness.

Your pulse may be small enough as to not to allow the LED current to be
exceeded.

You should check the current on the LED.  It may work for a while, but if
you are putting it in a product I would not recommend going over the
manufacturers specified limits.

In answer to your question....the 1k possibly is not needed :)

David


----- Original Message -----
From: Mel Evans <MEvans1027@AOL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, May 21, 2000 7:25 AM
Subject: PIC driving LED -- need series R?


> Hi, all --
>     I'm using an I/O pin (GP5) on a 12C671, running on 3V, to drive a
small
> 20 ma LED (Digikey P8037S) in series with a 1K current-limiting resistor.
> Drive pulses are 10 msec on, 500 msec off.  No other I/O is happening
during
> the pulses.
>     Is the 1K resistor really necessary?  It seems to work fine without
it.
>
> -- Mel Evans    mevans1027@aol.com
>